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Theory Manual
Physics and theory for nanoFluidX.
Physics
Learn more about the physics features in nanoFluidX.
Contact Angle
Enable the contact angle parameter to allow different wetting behaviors.

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Theory Manual
Physics and theory for nanoFluidX.
- Physics
  Learn more about the physics features in nanoFluidX.
  - Body Force
    The body force, defined through acceleration in units of [m/s²], can be varied over time using an input file.
  - Contact Angle
    Enable the contact angle parameter to allow different wetting behaviors.
  - Energy Equation
    Energy equation in nanoFluidX is implemented so that it accommodates for conduction and convection heat transfer with initial or Dirichlet boundary conditions.
  - Surface Tension - Multiphase
    nanoFluidX implementation of the multiphase surface tension model heavily relies on the work of Adami et al.
  - Surface Tension - Single Phase and Adhesion
    Both single phase surface tension and adhesion modeling is based on the work of Akinci et al.
  - Viscosity Models
    nanoFluidX now supports both temperature-viscosity and non-Newtonian modeling behavior. For temperature-viscosity, three models were implemented: polynomial, Sutherland, and power law. For non-Newtonian, the Cross model is available, which can be used to approximate power law behavior without risking instabilities due to viscosity unboundness of the power model.
- Boundary Conditions
  Learn more about the boundary conditions in nanoFluidX.
- Measurements
  Learn more about the measurements features in nanoFluidX.
- Solver Features
  Learn more about advanced solver features in nanoFluidX.
Validation Manual
Error and Warning Messages
This glossary contains generic messages generated by nanoFluidX, their likely causes, and possible methods to resolve the related issues.
Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding nanoFluidX.
Bibliography
References used throughout the nanoFluidX manual.

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Contact Angle

Enable the contact angle parameter to allow different wetting behaviors.

The default wetting behavior on walls for the TARTAKOVSKY2016_F1 surface tension model is neutral with a static contact angle of 90 degrees. Enabling the contact angle parameter allows simulation of different wetting behaviors in single phase flows (the only type of flows the model is currently recommended for).

Note: When using subphase-aware contact angle and TARTAKOVSKY2016_F1 surface tension model, the total number of cfg phases is limited to 100.

Contact angle is a single value prescribed as a solid surface/boundary property. This can be set via the parameter contact_angle in the phases subsection of the .cfg file for any WALL or MOVINGWALL phase and will be ignored for fluid phases. It is measured as the angle (

θ_{c}

) between solid and fluid surface with respect to the (resolved) fluid phase.

Figure 1.

An angle of less than 90 degrees develops hydrophilic behavior and an angle greater than 90 degrees develops hydrophobic behavior. Figure 2 illustrates this with a droplet on a flat surface with contact angles of 30, 60, 90 and 120 degrees.

Figure 2.

Figure 3 contains isometric, plan, and elevation views of three droplets with equal volume. From left to right the droplets are assigned contact angles of 30, 90 and 120 degrees. This illustrates that contact angle affects the particle spread and distance from the wall.

Figure 3.

Wetting behavior is highly sensitive to numerical (particles aligned on a Cartesian grid) and experimental (surface type and cleanness) setups. This parameter should not be interpreted as a precise parameter down to a single degree, but rather an estimate of the wetting behavior in general (wetting/non-wetting to certain degrees).